By means of metallization, contacts to semiconductor devices are created. In this respect, the metallizations must meet a number of preconditions in order to be able to be employed in semiconductor technology. In addition to good adhesion to the respective semiconductor layer, such as silicon (Si) or silicon carbide (SiC), a high level of current-carrying capacity, low electric resistance, low contact resistance between the metallization and the semiconductor, as well as ease of patternability of the metallization are also desirable.
For manufacturing patterned metal contacts, e.g. on SiC devices, so-called lift-off technique may be employed. It involves initially applying a suitably patterned resist mask to the SiC device and subsequently applying the desired metallization layer. In a subsequent step, the resist mask is removed along with the metallization located thereon. Thus, a patterned metal contact is formed on the SiC device, comprising the image of the negative resist mask. The production of thick metal layers of thicknesses of, for example, more than 200 nm, may be critical or impossible in this context, since thick oxides and resist masks are required, and/or since irregular breakage edges would result.
In addition, the risk of contamination of the semiconductor surface by metal particles or by the wet-chemical process of removing the resist mask along with the metallization layer is very high. In particular with surface-sensitive devices such as Schottky diodes, this may lead to high yield losses in production. For the metal deposition before the lift-off process, only a method with an anisotropic deposition characteristic should be employed, since otherwise an edge covering of the resist mask, or lift-off mask, will occur.
Another possibility of applying patterned metal contacts onto semiconductor devices is given by masked etching techniques, such as wet-chemical etching or plasma etching. However, this may also give rise to problems. For example, wet-chemical etching may cause undesired local underetching because of adhesion problems of the photoresist mask. The metal edge may be formed in an irregular manner, and small patterns may no longer be realized in a reliable manner. In plasma etching, an etch stop, i.e. a high etching selectivity, of the metal to the SiC or auxiliary layers such as oxides can hardly be realized. In addition, the exposed semiconductor surface may be damaged by the plasma etching process.
Therefore, what would be desirable is an alternative method for achieving a locally patterned metallization for manufacturing, for example, a SiC device without having to accept the above-mentioned disadvantages.